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Replacing a defective hermetic compressor that is noisy and not pumping. The refrigerant that was used was Hot Shot. The oil in the new compressor is Polyester and I want to use R404 or R134 for proper oil return. The unit is Medium cool and the thermestat is usually set at about 38 degrees.
The present compressor CS20K6E TF5-270 was not a burnout, just defective valves and not pumping at all. Both suction and discharge same pressure, The unit is 3 phase. Will change both suction and liquid filter driers and blow lines out with nitrogen.

404A or 134A

What was the original refrigerant used in the system (before Hot-Shot) go with that. Flush out the system,then use suction and liquid line driers. Also when charging it is now reccomended to charge liquid through a drier after evacuating to 500 microns(no lower compressor oil boils at 200 microns).

I think you need to call Copeland to make sure you have the correct compressor. 134a and 404a are for different applications, and run different pressures. If the refrigerant was Hot Shot, then it was probably R12, so 134a is probably what you want. You need to check that the evaporator and condenser is properly sized if you're changeing to 404a, and also change the TXV.

I understand that, but each compressor is rated for different applications such as "medium temp 134a," "low temp 134a" and "low temp 404a." Just because the refrigerant is compatible with the oil, doesn't mean that it will act correctly in the application.

Basically, 134a is a replacement for R12, and 404a is a replacement for 502. You wouldn't put R12 into a 502 system, as it wouldn't work. In the same respect, 134a would not work properly in a 404a system.

You said that it was a medium temperature compressor. It's not often that you see 404a used in a medium temperature application, and since you said that the old unit had Hot Shot in it, I'd assume that you need 134a.

404A or 134A

Extended means it will cover a greater btu rating. Tecumseh calls theirs the plus line ie 1/3+ 1/4 + for a little more btu rating. If it had "Hot-Shot" in it, then the previous mechanic did not do his home work like you did. Then you must flush the system, remove the expansion valve or if a capillary tube system back flush it.

Hold your horses now, guys.........

As I read this thread, it has yet to be established what refrigerant this system was originally set up for. (We all know it wasn't built for Hot-Shot).

There's no nameplate info given or TXV identifiers noted anywhere. We don't even know if this compressor is a proper replacement for the job.

It was mentioned that this CS20K6E is multi-rated for R134A HT, R22 MT and R404A EMT (Extended MT). The original post says this is a cooler, so if you check capacities at +20ºF SST/ 120ºF SDT for each of these refrigerants we find that R22 and R404A are about equal at 20,000 Btuh and R134A comes in at around 12,000 Btuh. That's a big difference.

We need a lot more info on this system before we start recommending what refrigerant to be putting in it.

Sgosine557.....How about some info on the TXV, the evaporator coil or the original condensing unit dataplate?